The invention relates to a radiation diagnostic apparatus for generating tomographic images of an exposure subject with a positioning means for positioning the subject with a measuring arrangement for the irradiation of the exposure subject from different directions consisting of a radiation source which emits a radiation beam penetrating the layer to be examined, the dimension of said radiation beam perpendicular to the layer plane being substantially equal to the layer thickness and of a radiation receiver which supplies electric output signals corresponding to the measured radiation intensity and with a computer connected to the radiation receiver for calculating the attenuation values of specific image points of the irradiated body layer from the output signals of the radiation receiver.
In known radiation diagnostic apparatus of this type, socalled computer tomographs, x-ray tubes are provided as the radiation sources, which x-ray tubes emit a bremsstrahlung spectrum whose center of energy is displaced toward higher radiation energies by means of the self-absorption of the x-ray tube wall and by means of filters which serve for reducing the exposure of the patient to radiation. Nevertheless, in practice, the spectral distribution is still so wide that, upon the irradiation of the patient, a further radiation hardening ensues which depends on the thickness and on the composition of the irradiated subject. For the production of an image from the output signals of the radiation receiver, this varying radiation hardening within the patient has as a consequence that
a correction according to this radiation hardening must be made for the sake of uniformity of the image and, above all, for a quantitative image evaluation; PA1 varying energy dependency of the beam detectors must either be avoided or likewise be corrected; PA1 fluctuations of the mean energy of the spectrum emitted from the radiator (including the filtering means associated with the x-ray source) must either be held sufficiently small or be likewise corrected.